1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a pixel structure that increases response speed of liquid crystal.
2. The Related Arts
A liquid crystal display (LCD) is a flat and ultra-thin display device that is composed of a number of color or monochrome pixels arranged in front of a light source or a reflection surface. The liquid crystal display has a very low consumption of power and is thus favorable to engineers for being applied to electronic devices powered by electrical cells. The principle is applying electricity to stimulate liquid crystal molecules to generate points, lines, and surfaces that work in combination with a back side lighting tube to constitute an image.
It is known that human eyes have the phenomenon of “persistence of vision”, which is a temporal illusion of an image of high speed movement persisting in human brain. Motion pictures and movies, and the recently developed games are applications of the principle of persistence of vision, by which a series of gradually changed pictures that are displayed fast and continuously in front of the human eyes form a dynamic image. The displaying speed of pictures that human being can perceive is 24 pictures each second. This is the reason that movies are shown with a speed of 24 frames each second. If the displaying speed is lower than this level, pauses of pictures and discomfort will be perceived by human beings. Based on such a criterion, each picture must be displayed for a time period shorter than 40 ms. Consequently, for a liquid crystal display, a response time of 40 ms is a threshold. Any displaying device having a response time higher than 40 ms will display phenomenon of “trailing image” or “image sticking”. Thus, the first factor that is taken into consideration by general consumers in purchasing a liquid crystal display or a liquid crystal television is the response time of liquid crystal.
The response time is the speed that each pixel of a liquid crystal display responds to an input signal and is the time interval that a pixel turns from dark into bright or from bright into dark. The commonly mentioned 25 ms and 16 ms are exactly the response time. The shorter the response time is, the less the image trailing will be perceived by a viewer in viewing a dynamic image. The principle is to apply electrical voltage to a liquid crystal box to have the liquid crystal molecules twisted and restored. Referring to FIGS. 1A-1C, schematic views illustrating the twists of liquid crystal under electric fields of various intensities are given. When the electric field has a strong intensity, the liquid crystal is approximately horizontal, where the image is brightest. When the electrical field is of a weak intensity or is null, the liquid crystal is approximately vertical, where the image is darkest.
Factors that affect the response time of liquid crystal can be classified as two categories:
(1) material of liquid crystal, including the thickness of liquid crystal inside the liquid crystal box, the dielectric constant of liquid crystal, viscosity of liquid crystal, and elastic constant of liquid crystal; and
(2) action between light guide plate and external force, including the intensity of electric field externally applied to liquid crystal and alignment power of alignment layer.
The continuous progress of technology brings constant improvement of LCD techniques and it is now a challenge topic of the development of liquid crystal displays to further improve the response speed of liquid crystal in order to take an invincible foundation in the LCD business.